In this article, factors that influence magnetic resonance imaging (MRI) radio-frequency (RF)-induced heating and voltage for patients with active implantable medical devices (AIMDs) are analyzed based on the transfer function method and the transmission line model. The influence of each factor is analyzed in the form of transmission line coefficients and impedances. These factors include factors of the media environment and factors of AIMDs. The analysis of the media environment factors provides insights into the tissue-simulating medium selection, and the analysis of AIMD factors can help the design of MRI conditionally safe AIMDs.